As is described in U.S. Pat. No. 8,958,694 to the General Instrument Corporation, which is incorporated by reference herein in its entirety, modern cable telecommunications systems are typically built with a Hybrid Fiber Coaxial (HFC) network topology to deliver services to residences and businesses. The HFC network is capable of carrying multiple types of services including one or more of: analog television, digital television, video-on-demand, high-speed broadband internet data, and telephony.
By using Frequency Division Multiplexing, multiple services on these systems are carried on Radio Frequency (RF) signals in the 5 MHz to 1000 MHz frequency band. The HFC topology carries the RF signals in the optical domain on fiber optic cables between the headend/hub office and the neighborhood, and then carries the RF signals in the electrical domain over coaxial cable to and from the home. The fiber optic signals are converted to and from electrical RF signals in a device called a fiberoptic “node.” In the coaxial portion of the network, the signal is split to different housing areas and then tapped off to the individual homes by a bi-directional coupler, which is otherwise referred to as a “tap.” The taps of the network connect the homes in a tree and branch configuration off of the node.
The RF signals continue to be delivered through the home on coaxial cables and are connected to devices in the home. Due to attenuation in the coaxial cable and split/tap losses, “RF amplifiers” are used periodically to amplify the electrical signal so that it is at an acceptable level to be received by the devices at the home.
Information is transported from the headend/hub office to the home, such as video, voice and internet data, over the HFC network. Also, information is transported back from the home to the headend/hub office, such as control signals to order a movie or internet data to send an email. The HFC network is bi-directional, meaning that signals are carried on the same network from the headend/hub office to the home, and from the home to the headend/hub office. The same coaxial cable carries the signals in both directions. In order to do this, the frequency band is divided into two sections, “forward path” and “return path,” so there is no interference of signals. The “forward path” or “downstream” signals, which typically occupy the frequencies from 52 MHz to 1000 MHz, originate in the headend or hub as an optical signal, travel to the node, are converted to electrical RF in the node, and then proceed to the home as electrical signals over coaxial cable. Conversely, the “return path” or “upstream” signals, which typically occupy the frequencies from 5 MHz to 42 MHz, originate in the home and travel over the same coaxial cable as the “forward path” signals. The electrical signals are converted to optical signals in the node, and continue to the hub or headend over fiber optic cables.
Referring back to the taps of the HFC network, a conventional tap 10 is shown in FIGS. 1-3. The tap 10 includes a housing 7 having a line input port 12, a line output port 16, a plurality of drop output ports 20, and a series of directional couplers 11a-11d (referred to collectively as directional couplers 11) contained within an interior space of the housing 7. The directional couplers 11 are connected in series between the line input port 12 and the line output port 16, as shown. Each directional coupler 11 is also connected to a respective drop output port 20.
In operation, an input forward path RF signal line 8 is mechanically and electrically connected to the line input port 12. An output forward path RF signal line 14 is mechanically and electrically connected to the line output port 16. Drop cables 18 are mechanically and electrically connected to the respective drop output ports 20. As shown in FIG. 2, the input forward path RF signal line 8 distributes a 52 MHz to 1000 MHz forward path RF input signal 13 into the tap 10. The forward path RF signal 13 passes through the directional couplers 11 within the tap 10. As the forward path RF signal 13 passes through each directional coupler 11, tapped forward path RF signals 19 (each at −26 dB relative to the forward path RF signal 13) are output through respective drop cables 18 in the downstream direction to respective homes (or other devices or locations). The forward path RF output signal 15 (at −1 dB relative to the forward path RF input signal 13) is output through the line output port 16 of the tap 10. The forward path RF output signal 15 is then distributed through the output forward path RF signal line 14 in the downstream direction to a further tap (or other device).
Referring now to FIG. 3, the tap 10 is also configured to deliver 5 MHz to 42 MHz return path input signals in the upstream direction. In operation, the 5 MHz to 42 MHz drop return path input signals 21 are delivered from respective drop cables 18 into the tap 10, through one or more directional couplers 11, and a resulting output return path signal 22 (at −26 dB relative to the drop return path RF signal 21) is delivered into the RF signal line 8, and into the node (not shown) that is connected to the RF signal line 8. A 5 MHz to 42 MHz return path RF input signal 23 is also delivered from the RF signal line 14 into the tap 10. The return path RF input signal 23 passes through the directional couplers 11, and the resulting output return path signal 26 (at −1 dB relative to the return path RF input signal 23) is delivered through the RF signal line 8, and into the node (not shown) that is connected to the RF signal line 8.
The tap 10 is a directional component that is intended to be operated in one direction only (i.e., forward path downstream and return path upstream) due to the design of the directional couplers 11 within the tap. In other words, the input forward path RF signal line 8 can only be connected to the line input port 12. If the input forward path RF signal line 8, which carries a 52 MHz to 1000 MHz signal, were mistakenly connected to the line output port 16 of the tap 10, then the tap 10 would not operate properly. The signals on the drop cables 18 would be significantly degraded or non-existent.
In the event of a redesign of an existing HFC network, such as by adding additional nodes to the network, a forward direction RF signal could be delivered through the coaxial cable and the taps in a direction that is opposite the direction over which the RF signal was delivered prior to the redesign. In other words, due to the redesign, the forward direction RF signal line would be connected to the line output port of an existing tap. Due to the above-described directionality limitation of the taps, the redesign would necessitate either time-consuming re-cabling to/from the tap (i.e., to connect the input forward path RF signal line 8 to the line input port of the tap and connect the line output port of the tap to the cable 14) or costly replacement of the faceplate of the tap to reverse its directionality. In view of the foregoing, there exists a need for easily reversing the directionality of a tap.